Multi-strand post-tensioning systems are used in a wide variety of applications. Conventionally, such systems are used for all types of slabs in buildings, bridge decks, and similar applications. Typically, a plurality of strands are placed so as to extend through ducts. The ends of the strands which extend outwardly of the ducts are placed into anchorages. The strands are stressed and locked-off individually. The post-tensioning of such systems enables slab deflections and cracks under severe service conditions to be kept under control. This permits larger spans and thicker slabs to be used. The reduced materials and labor results in lower costs and faster construction. Additionally, there can be indirect savings on foundations, columns, walls and vertical surfaces.
In normal use in such existing multi-strand post-tensioning systems, the ends of the strand will extend through separate holes formed in an anchorage body. Typically, a plastic trumpet will interconnect the anchorage body to the flat tendon-containing duct. The strands will extend through tapered holes formed in the anchorage body. Normally, the strands will be angularly offset from one another as they extend through the anchorage body.
After installation, wedges are placed around the exterior of each of the outwardly extending strands. A jack is used so as to stress the strands. The wedges will remain in contact with the strands during the stressing operation. After the jack has sufficiently stressed the strands, the pressure in the jack is released so that the wedges automatically seat in the conical holes of the anchor head.
After the strands are wedged into the holes of the anchor, it is then necessary to grout the interior of the anchor and the interior of the duct. In order to facilitate the grouting of such duct, a grout hole is machined into the body of the anchor. Under existing systems, a hole is drilled and tapped through the body of the anchor so as to communicate with the interior of the duct. After the hole is machined and tapped, a special fitting is installed so as to connect a grout tube with this hole. The grout tube is then free to pass grout into the interior of the duct so that grout can be used to fill the interior of the duct and to solidify on the interior of the duct. Normally, the drilled and tapped hole in the anchorage body extends transverse to the tendon-receiving passageways so as to open on a top surface of the anchorage body. After the grout is pumped into the interior through this machined hole, the grout tube must be removed from the fitting and the hole should be sealed.
Unfortunately, the forming of such a grout hole makes the anchor very expensive. Under conventional circumstances, the anchor is made of a cast metal. The machining and forming of the grout hole on such anchorages is a time consuming and expensive operation. Often, the machining operations required so as to form the grout hole can double or triple the cost of the anchor body itself. As such, a need has developed in which to provide a grout hole on such multi-strand post-tensioning systems which is less expensive and easier to use.
FIGS. 1-3 illustrate a conventional prior art anchor as used in a multi-strand anchorage system. It can be seen in FIG. 1 that the anchor body 10 has a flanged back surface 12 which extends to an interior tendon-receiving passage 14. Grout hole 16 is formed through one of the gussets which extend from the tendon-receiving passage 14 to the flanged anchor body 12. As can be seen in FIG. 3, the grout hole 16 is drilled and tapped so as to receive the threaded fittings of a grout tube. FIG. 2 is a side view of the anchor body 10. In FIG. 2, it can be seen that the flanges 12 of the anchor body 10 extend outwardly from a central tubular area 18. The tendon-receiving area 14 is formed on the interior of the tubular area 18. FIG. 3 shows this prior art system as taken across lines 3--3 of FIG. 1. In particular, it can be seen that the grout hole 16 is formed in the surface 20 of the anchor body 10. The grout hole 16 includes a threaded area 22. The threaded area 22 is adjacent to the opening 24 on the surface 20 of the anchor body 10. The threaded area 22 includes female threads which are suitable for receiving the male threads of a fitting of a grout hole. Typically, the threaded area 22 is formed initially by drilling a hole into the surface 20 of the anchor body 10 and then tapping the hole. A curved passageway 26 will extend from the threaded area 22 so as to open at outlet 28. Outlet 28 serves to deliver grout to the tendon-receiving area 14 of the anchor body 10. The curved passageway 26 is typically formed in the casting of the anchor body 12.
As can be seen in FIGS. 1-3, the formation of the grout hole 16 is a rather complicated matter. Initially, steps must be taken so as to properly form the curved passageway 26 during the casting of the anchor body 10. After this curved passageway has been formed, then it is necessary to carry out machining operations so as to form the threaded area 22. These machining operations are quite complicated and time consuming. Finally, after the machining operations are completed, it will be necessary to threadedly affix a grout tube to the threaded portion 22 of the grout hole 16. In many circumstances, the threaded fitting on the grout tube will not properly align with the threads 22 on the grout hole 16 so as to create an improper connection between the grout tube and the anchor plate 10. This can cause the improper and leaking transmission of grout to the tendon-receiving area of the anchor plate 10.
In addition to the costs of forming the threaded area 22 on the anchor plate 10, there is an additional cost of forming a threaded fitting on the end of a grout tube. Normally, a metal threaded fitting is affixed to the elastomeric grout tube. The formation of the threaded fitting and the attachment of the threaded fitting to the grout tube is often a costly and time consuming proceeding. As such, a need has developed in which to form a grout tube which includes the necessary structure so as to allow the grout tube to be properly affixed to the grout hole of the anchor plate.
It is an object of the present invention to provide a post-tensioning system which allows for the easy attachment of a grout tube to the anchor plate.
It is another object of the present invention to provide a post-tensioning system which eliminates the need for machining operations on the anchor plate casting.
It is another object of the present invention to provide a post-tensioning system which eliminates the need for forming and attaching fittings to the grout tube.
It is still another object of the present invention to provide a post-tensioning system which simplifies grouting procedures, reduces costs, and eliminates unnecessary equipment.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.